This invention relates generally to hot water circulation systems that rapidly deliver hot water from a conventional water heater to a hot water faucet and, more particularly, to such a system employing a two-way check/bypass valve for increased efficiency and performance.
The need for and benefits of making hot water rapidly available at remote faucets in residential buildings is well known. However, minimal progress has been made over the years toward implementation of systems satisfying that need. It has been estimated that the average home in America wastes up to 10,000 gallons of potable water each year as homeowners run cool water down the drain while waiting for hot water to reach a faucet remote from the water heater. Since the wasted water was once hot, the heat energy it contained is also wasted.
The time required for hot water to reach a remote faucet depends on the length of the line from the water heater to the faucet. In many buildings, the delay amounts to a minute or more. At a typical faucet flow rate, five to six gallons of water can be wasted several times a day at a given faucet.
Tests have shown that water in an un-insulated ¾-inch diameter copper pipe at a temperature of 118° F. in an ambient environment of 70° F., will cool to 100° F. in about twenty minutes. If the supply line is ½-inch in diameter, the temperature will drop to about 95° F. Water at a temperature of 100° F. is warm to the touch, but cannot be considered hot. The reintroduction of heater-temperature water to the system is necessary to deliver hot water at a faucet. A simple solution to this waste of water and heat energy is to establish a circulation flow of hot water from the existing water heater through the normal hot water distribution line to the most remote hot water faucet on the plumbing branch, and back to the heater. This can be accomplished using a dedicated return line from the hot water faucet line typically located under the sink to the water heater, or by routing the return flow into the normal cold water supply line back to the water heater. Contrary to the belief of the average plumber, engineering tests and analyses have proven that circulation systems will conserve heat energy as compared to standard systems without circulation.
Water circulation can be accomplished either passively or actively. Passive circulation systems rely on convection forces resulting from differential temperatures between the hot and cold supply lines, whereas active systems incorporate an electric pump and possibly electronics connected to an electrical outlet to control the pump and a valve. Connections that must be made to the water piping are somewhat more complex in the case of active water circulation systems.
Passive water circulation systems operate on the principal of convective flow, by which hot water will rise and cool water will fall in a closed loop, without the need of a pump. Since hot water cools as it travels away from the heater and since cool water is denser than hot water, a higher pressure will exist in the cold line. This higher pressure will cause a low level circulation flow from the heater up to the high point in the loop at the remote hot water faucet, so long as a vertical separation of a few feet exists between the water heater and the faucet. This vertical separation exists in the normal home in which the water heater is in the basement and the faucets are on the main or a higher floor. This low level flow rate is sufficient to maintain hot water at remote faucets, and will operate continuously, day and night, without attention. Convective circulation systems require no electrical power, no gas, and no burner, and operate reliably with few moving parts, based upon the laws of physics.
Convective water circulation systems will cool by only 15-20° F. in the loop to and from the water heater at a flow rate of about 240 cubic centimeters per minute. This temperature loss represents a smaller heat energy loss than the combined heat energy loss resulting from allowing previously heated water to go down the sink drain while the user waits for hotter water to arrive and the energy required to heat the replacement water entering the water heater at about 50° F.
Active circulation systems employ a pump, control circuitry, and complex mechanisms that are expensive and require a source of electrical power and a professional installer. They are less reliable than passive circulation systems since they utilize more components. In active circulation systems, the pump will start at a preset water line temperature or elapsed time in order to restore hot water at the remote hot faucet. Typically, the time interval between pump cycles will be on the order of twenty minutes. At the end of each pump cycle, the water at the faucet will be hot and will then gradually cool before the pump starts again.
With an emphasis on simple installation, industry trends have moved toward the use of the cold water supply line as the return loop for circulation in both active and passive systems, thereby avoiding the costly and sometimes difficult installation of a dedicated return line. Circulation can be achieved through the addition of a crossover line between the hot and cold supply lines under the sink. The circulation path is from the water heater through the normal hot water supply line, through the crossover line, into the cold water supply line, and back to the water heater. The crossover line must also provide a means to prevent mixing of hot and cold water when a faucet is opened.
A review of prior art water circulation systems that utilize the cold water supply line as a return line reveals that most of them utilize a standard one-way check valve in order to prevent cold water from flowing into the hot side of the system when the hot faucet is opened. Some prior art systems utilize either a thermostatically-operated or solenoid-operated valve to prevent that situation. Other prior art systems, such as those described in U.S. Pat. No. 5,819,785 to Bardini, U.S. Pat. No. 5,323,803 to Bluemenauer, and U.S. Pat. No. 6,779,552 to Coffman, for example, address the above problem, but fail to recognize the need to prevent hot water from flowing into the cold side of the system when the cold faucet is opened. Solenoid valves operated on a timed basis may avoid the problem, but thermostatically-controlled valves may allow hot water to flow into the open cold water faucet during a portion of the valve's operating cycle as it responds to changes in water temperature. Moreover, these prior art systems fail to recognize, that unlike waiting for hot water to arrive at a remote hot water faucet in systems without circulation, cold water will never flow from the cold water faucets. Without some additional provision, hot water will flow through the bypass line into the cold water line, and lukewarm water will be delivered at the cold water faucet. Finally, each of these prior art valves contains free poppets with no provision to avoid a water hammer effect upon closing.
The system described in U.S. Pat. No. 2,842,155 to Peters describes a valve using a thermostatically-operated ball for controlling convective flow, primarily in the direction from hot to cold, and a free ball check to prevent cold to hot flow when the hot faucet and the thermostatically-controlled ball are open. No provision to avoid a water hammer effect is provided in this valve.
U.S. Pat. No. 4,391,295 to Stipe describes a one-way, gravity-operated cheek valve for use in a convective hot water circulation system. A slow-closing valve with gravity reseating provides damping of valve closures that are otherwise noisy and potentially damaging. The slow-closing valve is a one-way valve for use in systems employing a dedicated return line and is of no usein systems returning water through the cold water supply line.
The present invention provides a high-performance, inexpensive, maintenance-free passive hot water circulation system for use in both existing buildings and new construction that eliminates the need for an expensive dedicated hot water return line and that may be packaged in kit form for easy installation by a homeowner. It utilizes a two-way check/bypass valve that is connected between the hot and cold water supply lines at hot and cold water faucets that are located most distantly from the water heater in a plumbing branch of a building. The two-way check/bypass valve establishes and maintains convective hot water circulation at a low flow rate from the water heater to the most distantly located hot water faucet, through the cold water supply line of the plumbing branch, and back to the water heater, during the period of time when both the hot and cold water faucets are closed. When the hot water faucet is opened, hot water is nearly instantly available. The two-way check/bypass valve stops convective hot water circulation when either the hot or cold faucet is opened. It also prevents mixing of hot and cold water when either the hot or cold faucet is open and includes provision for dampening any water hammer effect.